In tire uniformity machines, a tire is tested by rotating it at various speeds to ensure that the tire has been constructed and performs within quality control standards. During this testing process, the tire is rotated and the tire uniformity machine examines the tire""s shape and surface characteristics to a high degree of accuracy. At times, during examination, the tire uniformity machine detects irregularities in the tire. Any irregularity in the surface and shape of the tire may be corrected by removing material from appropriate portions of the tire.
To remove material, known tire uniformity machines typically employ a grinder having a single cylindrical grindstone rotating in relation to the rotation of the tire. As the tire rotates, the grindstone is selectively brought into contact with the tire to remove material.
In known grinders the application of the grindstone occurs in a rotary fashion. The typical grinder has a pivoting arm on which the grindstone and its motor are mounted. Often a motor and gear box arrangement is used to control the speed and direction of rotation of the grindstone. The motor is then connected to the grindstone or gearbox by belts or chains and a series of pulleys or sprockets. As will be appreciated, the motor needed to drive the series of belts or chains and the gear box are bulky and the available area for positioning of this unit is limited. In fact, the typical motor housing projects to such an extent that the confines of the tire uniformity machine prevent the grindstone from being actuated in a linear fashion. To overcome this, known tire uniformity machines attach the motor distally from the grinder on an arm that houses the drive belt or chain. In this way, the motor is located away from the instrumentation, the load wheel, and other devices that must be placed proximate to the test tire, where there is more space. The arm is mounted on a pivot such that the motor housing moves radially in a limited area. The pivot is located between the motor and grindstone, and the arm rotates under the force of a hydraulic cylinder attached to the arm on one side of the pivot. The typical hydraulic cylinder acts transversely of the arm and, thus, is mounted on a separate frame member than the frame member on which the arm pivots. So mounted, the hydraulic cylinders reduce visibility and access to the grinder and the area surrounding the grinder.
Due to the rotation of the arm, the grinder may not be aimed directly at the tire center. In other words, the center line and the contact point of the grinder travel in an arc in an attempt to tangentially contact the tire. As will be readily understood, initiating contact with the tire in this manner makes it difficult to make good, accurate contact in a repeatable manner. Further, the housing of the grinder must be adjusted to clear the machine housing and attempt to make proper contact between the grinder and the tire. Specifically, the grinder housing often is connected to a vacuum supply to remove particles created by the grinding process, and this housing must be made to closely fit about the grindstone. Since the housing closely fits about the grindstone, in these devices, simple rotation of the arm may cause the housing to contact the rotating tire. As will be appreciated, such contact could significantly damage the grinding apparatus and may cause damage to the tire.
To avoid such contact and to better position the grindstone to remove material, known devices adjust the position of the housing and grindstone by rotating the housing relative to the arm. To make this adjustment, known devices incorporate a series of linkages. In some cases, as many as five linkages may be used. Due to machining tolerances, each link is a potential source of error. When multiple links are used, this error is compounded making it more significant in terms of accurate removal of the tire material. These errors make it difficult to achieve good contact with the tire.
Also, when two grinding stones are used, it virtually eliminates the grinder""s ability to have both stones strike the tire simultaneously; and some cases may cause one stone to be out of contact with the tire T. A second stone is often used in an attempt to remove a lip or other irregularities created by the leading stone, as described more completely below. When linkage errors result in the trailing stone not being in contact with the tire, the trailing stone is precluded from performing its corrective function.
In known grinders, the amount or rate of material removal from the tire is often measured as a function of the grind current of the single motor driving the stone or stones. In a two-stone apparatus, the grind current measurement, of the single motor, would not be able to provide information on the percentage of work done by each grinder, and thus, if one stone was completely out of contact, this condition would go undetected. Further, the components linking the motor to the grindstones including belts or chains introduce additional error into this measurement.
Turning to the removal of material from the tire, known devices typically employ a generally cylindrical grindstone that rotates about a central axis of rotation. As best shown in prior art FIG. 1, the radial profile of the cylindrical grindstone leaves a lip L at each break in the periphery of the tire at the leading side, with respect to grindstone rotation, of the tire elements E, where the grindstone has made contact. It is believed that the lip L is formed by the rotation of the grindstone. As the grindstone encounters tire elements E separated by breaks in periphery of the tire T, the radial force of the stone causes deformation of the tire element E in the radial direction. At the same time, the tangential force of the stone acting on the relatively weak, generally flexible tire element E causes the tire element E to bend in the direction of the grindstone""s rotation. Thus, the leading portion of the tire element E is ground to a lesser extent because it has been deflected away from the grindstone. Once the element is past the grindstone, the deflected element returns to its resting position with an irregular profile, as shown in FIG. 2. This irregularity is often referred to as a lip L.
In a single stone apparatus, attempts have been made to remove the lip by reversing the rotation of the tire and grinding in the opposite direction. Unfortunately, the result of this reversal is a corresponding lip on the opposite side of the tire element. Dual grindstones were introduced as an attempt to use a second grindstone to remove the lip. As described above, the error introduced by linkages that adjust the position of the grinding head, however, interfered with proper contact of the grindstones resulting in incomplete removal of the lip L. Or, in cases where the second stone did not contact the tire, the lip L remained completely intact.
In either the single stone or dual stone apparatus, the pivoting attachment of the arms supporting the grindstones can be a source of inaccuracy when grinding the tire. As previously discussed, the grinder is typically mounted on an arm that is pivotally attached to one of the frame members such that the grinder is rotated into contact with the tire. Typically, when the grindstones are in contact with the tire, the arms supporting the grindstones and extending back to the pivot point extends at an angle from the pivot. Forces at the grindstones are transmitted along this arm to the pivot. As will be appreciated, the length of the arm proportionately increases the moments on the pivot created by these forces. Unless the pivot is made extremely rigid, these forces may cause the arm or the grind head itself to move such that the grinders do not remove the appropriate amount of material. To avoid inaccuracies caused by such movement, a more stable system for mounting the grinder is needed.
It is an object of the present invention to provide a more stable mounting assembly for a grinder in a tire uniformity machine.
It is a further object of the present invention to provide a grinder assembly having a motorized tilt adjuster.
In general the present invention provides a grinder in a tire uniformity machine having a frame including a first side frame member and a second side frame member, the frame receiving a tire having a central axis for testing, the grinder including a carriage pivotally attached to the first side frame member and a locking assembly adjacent the carriage and the second side frame member selectively coupling the carriage to the second side frame member when the carriage is in the operating position; a grinding head supported on one end of the carriage, said grinding head having at least one grinding stone and at least one motor coupled to the grinding stone capable of causing rotation thereof.
The present invention further provides a tilt adjustor in a tire uniformity machine that tests a tire having a circumference, the tire uniformity machine having a grinding head supported on an arm at a pivot and pivotable about a pivot axis extending through the pivot parallel to a tangent of the circumference of the tire, the tilt adjustor including a motor assembly supported on the arm and operatively coupled to the grinding head, whereby activation of the motor assembly causes the grinding head to pivot.